Ok, I have four new terra grapplers 325 70r17, they measure out at a true 35. I picked up a couple used bfg a/t 315 70r17 that measure out at 34.5. Am I going to be safe using these as a spare in case of emergency? I only plan to use them to get me home so I can get the others repaired or replaced.

I know it's not perfect but is it safe?

 

Bump Ttt...

 

You would be fine IMO. There isnt that much difference in size, and to just use in case of flats I dont see a problem. On my old TJ (now my sons) he has 35's on all fours and a 33inch spare.

 

To use it as a spare to get home incase you blow your tire on the trail, sure.... However, I don't think its a good idea to run 2 differently sized tires for an extended period of time, regardless if the difference is minimal. Also keep in mind the weight of the tires will differ brand to brand, tread pattern will vary, along with the size - which will all effect how much it will take to spin them. Your tires will be spinning at different rates, asking more of your differentials, which in turn could make them fail prematurely. Again, if you wanna use it to get back from the trails and then get a new matching tire, I think you will be ok.... putting 1,000's of miles on your rig with this setup, not so good of an idea.

 

Thank you. I just plan to use it to get home in case of emergency.

 

It's safe. The difference between an actual measurement of 34.5 to an actual measurement of 35 is no different than using a new 35 opposite a high mileage 35. Your biggest handling issue will be from the differing tire brand/construction and tread but it is much better than a spare of a different size.(shorter/taller)

If you have a rear flat 100 miles from home and are still worried about damaging a LSD diff or wicked handling locker with two different diameters you can always put the spare on the front and the front "matching" tire on the rear.

Jer